Sodium-deficient O3-type Na0.83Cr1/3Fe1/3Mn1/6Ti1/6O2 as a new cathode material for Na-ion batteries

A novel Na-deficient O-3-type layered material Na0.83Cr1/3Fe1/3Mn1/6Ti1/6O2 has been synthesized via solid-state reaction and utilized as a cathode material for sodium-ion batteries (SIBs). It delivers initial charge/discharge capacities of 168.5 and 161.4 mAh g(-1) within the voltage range of 1.5-4.1 V at current rate of 0.1C. A phase transition pathway of O3 -> O3 '' O3 -> O3 '' is revealed during the initial charge process by ex situ X-ray diffraction. In addition, synchrotron X-ray absorption spectroscopy suggests that the charge compensation of Na0.83Cr1/3Fe1/3Mn1/6Ti1/6O2 during the initial charge and discharge processes is contributed by Cr3+/Cr4.3+, Fe3+/Fe3+-4+ and Mn3+-4+/Mn4+ redox couples. The local electronic structure of layered Na1-xCr1/3Fe1/3Mn1/3-xTixO2 (x = 0, 1/6, 1/3) is proved to have a great impact on the electrochemical performance. After coating carbon layer with similar to 10 nm, Na0.83Cr1/3Fe1/3Mn1/6Ti1/6O2 C exhibits the improved electrochemical performances regarding capacity retention and rate capability. (c) 2018 Elsevier Ltd. All rights reserved.